The area that connects my neck to my shoulder (towards lower left back of neck/near shoulder) seems more swollen and feels firmer. What are causes?

Spasm. One likely cause could be spasm of the muscle there. It would be best to see a doctor to have it checked out.
See below. This is a problem that requires a face-to-face meeting with your doctor. In that meeting, your doctor will listen to you, perform a throrough examination and possibly order labs or other tests. Based on this information, he/she will be able to tell you what's wrong and what to do about it.